WASHINGTON (CNN) -- Pope Francis immediately dove into the whirlpool of U.S. politics on Wednesday, using his first direct address to the nation to weigh in on deeply divisive issues including climate change, Cuba, marriage and immigration.
The pontiff, speaking before 11,000 ticketed guests at an elaborate welcoming ceremony on South Lawn of the White House, signaled he will not steer clear of controversial issues during his six-day visit. He climbed aboard an open-sided Popemobile later in the morning to parade before tens of thousands of cheering people lining the streets around the White House.
In remarks delivered slowly in accented English at the White House, Francis said he was ready to listen to the "hopes and dreams of the American people" and to offer guidance to those charged with shaping the nation's political future "in fidelity to its founding principles." And in comments that could antagonize Republicans, Francis endorsed President Barack Obama's efforts on climate change and rebuilding ties with Cuba after more than half a century of estrangement.
He said it was "encouraging that you are proposing an initiative for reducing air pollution. Accepting the urgency, it seems clear to me also that climate change is a problem that can no longer be left to a future generation."
"When it comes to the care of our 'common home' we are living at a critical moment of history," he said.
Francis is using the occasion of his visit to the United States to emphasize the core theme that has underpinned his two-year papacy: challenges like climate change, income inequality and the plight of immigrants are moral -- not political -- issues. And, he said, the richest, most developed countries have an obligation to act.
"I would like all men and women of good will in this great nation to support the efforts of the international community to protect the vulnerable in our world and to stimulate integral and inclusive models of development," Francis said, in comments that reflect what he sees as a more inclusive vision of capitalism.
While some of this themes were sure to please the left, he also delivered a firm defense of traditional values, warning that the institution of marriage and family needed to be protected at "a critical moment in the history of our civilization." Those remarks could irk liberals months after the Supreme Court ruled in favor of same-sex marriage nationwide.
He said that it was right that society was "tolerant and inclusive" but warned that American Catholics were "concerned that efforts to build a just and wisely ordered society respect their deepest concerns and their right to religious liberty. That freedom remains one of America's most precious possessions."
Obama gently -- but pointedly -- argued that "here in the United States we cherish religious liberty."
Stepping into another delicate political issue, the Argentine-born Francis noted that he was a "son of immigrants" -- a sign that he could address the heated immigration debate later in his visit.
Obama and first lady Michelle Obama earlier greeted the Pope at the White House as he stepped out of his small black Fiat, which he is using to make a statement of humility in Washington, a city full of limos and hulking government SUVs.
On a glorious early-fall morning, the President and Pope stood together before an honor guard as a band played the national anthems for the Vatican and the U.S.
Obama paid warm tribute to the Pope as an individual as well as the leader of 70 million U.S. Catholics, saying he displayed "unique qualities" of a leader "whose moral authority comes not just through words but also through deeds."
The White House has said that Obama will not seek to exploit the visit of Francis for political gain -- but the president warmly welcomed the pontiff's support on climate change and Cuba, for which he is trying to build domestic support.
"Holy Father, we are grateful for your invaluable support of our new beginning with the Cuban people, which holds out the promise of better relations between our countries, greater cooperation across our hemisphere, and a better life for the Cuban people," Obama said.
The president also said the Pope had offered reminders that "we have have a sacred obligation to protect our planet."
"We support your call to all world leaders to support the communities most vulnerable to a changing climate and to come together to preserve our precious world for future generations."
Obama and the Pope then held a private meeting in the Oval Office, which the White House said covered issues including the refugee crisis in Europe and the need to end extreme poverty within a generation.
The president presented his guest with a one-of-a-kind gift: a sculpture of an ascending dove made from metal taken from the Statue of Liberty and wood which once grew in the White House garden.
Francis also spoke to a gathering of U.S. bishops at The Cathedral of St. Matthew the Apostle in Washington, seeking to offer counsel at a time of great upheaval among his American flock which has thinned partly because of child sexual abuse scandals.
"I know how much the wounds of these last few years have weighed on your spirit, and I have supported your generous commitment to bring healing to victims -- in the knowledge that in healing, we too are healed -- and to work to ensure that such crimes will never be repeated," Francis said.
The Pope's visit is grinding Washington to a halt. Massive crowds greeted the pontiff as he emerged from the White House complex, standing five or six deep on sidewalks. Several times, his vehicle, a converted white Jeep Wrangler, slowed so the Pope could bless a small child handed to him by a security agent.
In front of and behind the Popemobile, police motor cyclists and black armored Secret Service vehicles fanned out -- evidence of a massive security operation being mounted during the Pope's visit.
Francis' next political intervention could come on Thursday when he makes an address to a joint meeting of Congress. He will travel to New York and Philadelphia later in the week to wrap up his six-day visit.
